Catalyst component-loaded honeycomb structures have been used in exhaust gas purification devices for heat engine (e.g. internal combustion engine) or burner (e.g. boiler), reformers of liquid fuel or gaseous fuel, etc. Also, it is known to use a honeycomb structure as a filter for capture and removal of the particulate matter contained in a particle-containing fluid such as exhaust gas discharged from diesel engine.
In such honeycomb structures used for the above purpose, non-uniform temperature distribution tends to appear inside owing to the sudden temperature change of exhaust gas or the local heat generation, which has caused problems such as cracking. In order to alleviate these problems, it was proposed to constitute a honeycomb structure in an integral structure of a plurality of honeycomb segments, by bonding individual honeycomb segments with an elastic bonding material, to relax the thermal stress applied to the structure.
In such a honeycomb structure formed by bonding a plurality of honeycomb segments, the outer wall of each honeycomb segment (to become a surface contacting with other honeycomb segments) was smooth. As a result, the bonding strength between honeycomb segments was weak, which has often caused, owing to the vibration or the exhaust gas pressure during the use, the loosening, movement or separation of honeycomb segments.
In view of the above situation, there was proposed a honeycomb structure of high durability formed by bonding, with a bonding material, a plurality of honeycomb segments each having a large number of through-holes which extended in the axial direction of honeycomb segment and which were surrounded by partition walls, in which honeycomb structure the smoothness of the outer wall of each honeycomb segment (to become a surface contacting with other honeycomb segments) was set at a particular level so that there was no movement of each honeycomb segment during the use owing to the vibration or the exhaust gas pressure (Patent Literature 1).
Cracking caused by thermal stress can be prevented to some extent by employment of honeycomb segments. However, it is considered that if each segment could have higher durability to thermal stress, reduction in cost or increase in regeneration efficiency could be possible owing to the reduction in the number of segments used.
In view of the above matter, there was proposed a honeycomb structure formed in one piece, using a plurality of honeycomb segments each having an outer wall, partition walls provided inside the outer wall, and a large number of through-holes (fluid passages) extending in the axial direction of honeycomb segment, surrounded by the partition walls, which honeycomb structure comprised honeycomb segments in which, in their sections vertical to the axial direction of honeycomb structure, each partition wall had an angle of 25° to 65° to a straight line along the outermost point of the outer wall contacting with other honeycomb segment and therefore which honeycomb structure had superior durability to cracking caused by thermal stress (Patent Literature 2).
Patent Literature 1: JP-A-2001-138416
Patent Literature 2: JP-A-2003-227327